They may be fine for now but soon they will begin to quarell as they try to set up their own territories. If you see a pair form then you can keep those two and hopefully they will be a mating pair and they will be happy fish in your tank But if this happens then take the other four back to the lfs as they will fight more and more as they get older and there is no way that your tank is big enough for 6 jd's, especially if they are all male
I would keep just the plec in with the jd's if they pair as they will most likely kill anything else in your tank when mating and after eggs are layed.
If you keep only one then you can try putting some other fish in with him/her but choices are very limited because of the hostile nature of jd's. Good luck though, and have fun with them! I love my JD
I have found my J.Ds to be reasonably peacful. I keep mine with ropefish, climbing perch and aurilis barbs. They rarely snap at the other fish, exept when they breed that is! Try having just a pair of the J.Ds with a shoal of bigger tetras, barbs or a few oddballs that could hold their own if the J.Ds breed. Bare n mind that all the new fish need to be at least 4" fully grown.